What is the operating temperature of the engine oil? Permissible boiling point limits for motor oil. How does overheating of oil in an internal combustion engine manifest itself?
The principle of operation of an internal combustion engine (ICE) is such that the result of its operation is a large release of heat. The heat inside the engine, especially in its cylinder-piston group, reaches 300°C and higher, if we consider diesel engines. Therefore, the engine oil temperature fluctuates widely as the lubricating fluid moves through the lubrication system inside the internal combustion engine.
Main functions of motor oils
A car engine has many components and parts. Their surfaces are constantly in contact, creating friction between themselves. The result of this phenomenon is increased wear. In addition, friction consumes a significant portion of the engine's efficiency, which is converted into heat.
High temperatures provoke expansion of the materials from which the parts are made. Expansion processes are accompanied by a decrease in the gap between the contacting surfaces. There will come a time when this gap simply disappears, and the internal combustion engine jams - this is what will happen if the unit operates without engine oil.
Engine oil performs a vital function, without which the unit simply cannot operate. It reduces the coefficient of friction by forming a thin oil film between contacting surfaces. In addition, lubricant increases engine efficiency and reduces wear of parts, promotes less heat generation, and also effectively removes it from rubbing surfaces. In addition to these functions, others are implemented:
The hydraulic fluid can also be controlled by pressure on hydraulic valve lash adjusters, hydraulic timing belt tensioners, and variable valve timing systems.
Lubrication system design
The most successful lubrication systems provide different amounts of lubricant, depending on the functional characteristics of the parts. Oil comes to the most critical components and parts under pressure. Less loaded areas receive it by splashing or natural flow. Such lubrication systems are usually called combined.
An oil pump is used to ensure the pressure of the working fluid inside the line. Experiencing such pressure, lubricating fluid from the engine crankcase is supplied to the oil filter. There it is cleaned and supplied to the bearings that ensure the rotation of the crankshaft. Next - to the piston pins, camshaft, valve rocker arms. If there is a turbine, the shaft on which it rotates will need oil. In addition, heat is removed from the inner surface of the pistons. The lubricant seals the gap between the oil scraper rings, as well as the piston compression rings and the engine cylinders, and prevents them from sticking. The liquid gets there, spraying from the nozzles at the bottom of the cylinder-piston block.
Next, the lubricant returns back to the oil pan. Along the way, it is sprayed by the crank mechanism, creating fog. It lubricates all the parts it envelops. From the mist, the lubricant condenses, returning to its original state and position. Thus, the cycle repeats again and again.
Temperature range of oil composition
The operating temperature of the oil varies widely - from ambient air to 180 degrees when passing through the cylinder-piston group. In this case, the metal surfaces of the pistons and cylinders are heated to 300°C. As it circulates through the engine, the oil composition tends to evaporate and burn away. To prevent hydrocarbon vapors from igniting inside the engine, it is necessary that their combustion temperature be higher than the one to which they are usually heated. This ability is determined by such an important parameter as the flash point of the oil.
To determine this parameter, the oil is placed inside the crucible. It is then heated until the fumes begin to flare from the flame. The temperature is immediately measured. Usually it ranges from 220°C and above. This is enough to prevent working fluid vapors from igniting inside the engine. This parameter is not critical, so manufacturers do not indicate on the canisters what the ignition temperature of the oil is.
By the way, diesel vapors ignite at a much lower temperature, about 55–60°C. Having effective water cooling, it is possible to reduce the upper temperature limit of the oil composition to 105–115°C, which is a fairly significant indicator.
Viscosity-temperature characteristics
The stability and efficiency of their operation depends on the viscosity characteristics of lubricants. Viscosity, as well as the viscosity index, are one of the most important indicators, since they change during the transition from very low (-40 ° C) to high operating temperature conditions of the power unit.
According to the classifier of the American Society of Automotive Engineers SAE, motor oils are winter (0W, 5W, 10W, 15W, 20W, 25W), summer (20, 30, 40, 50, 60), as well as all-season, which are commonly used everywhere - for example, 5W30 or 10W40.
The diagram shows the temperature ranges for using certain products. A very important indicator is the viscosity level in cold weather, as well as the pour point of the oil. That is, for example, 0W30 lubricant will allow you to start the engine at -40°C, ensuring its normal crankability. 5W30 will do the same down to -35°C and so on.
Overheating of lubricants is very dangerous for the engine. If the composition is heated to +125°C and above, it will lose its viscosity and will not be able to form an oil film. Therefore, it will penetrate into the combustion chamber through the piston rings, burning there along with the fuel. This is how soot deposits form and the lubricant burns out. That is why it is necessary to periodically check the oil level. It happens that a viscosity mismatch leads to lubricant consumption of up to 1 liter per 100–200 kilometers.
It is very important to use working fluids with the viscosity recommended by the manufacturer. This parameter can be determined from the service book issued for each vehicle.
During operation, the temperature of the oil in the engine heats up during operation, withstanding significant loads caused by the operation of its components and parts. Therefore, lubricants must be of high quality and meet operating conditions. To avoid bringing the engine oil to boiling point, you need to know what kind of lubricant to use.
Lubricating fluid is an important component for the operation of any engine. The document defining the classification and designation of oils used in internal combustion engines is the interstate standard GOST 17479-85, as amended in 1999. The requirements of this document are interrelated with the international standards SAE, API and ACEA, which determine the parameters of oils depending on the season and ambient temperature. The SAE standard defines the viscosity-temperature characteristics of a lubricant. The API standard specifies the use of lubricant, depending on the type of engine, its production date and technical parameters (for example, with or without turbocharging). The ACEA standard was developed by European manufacturers. It is similar to the API standard, but has more stringent indicators.
Based on the specified documents, motor oil can be gasoline, diesel and universal. The oil solution is made from mineral oil with the addition of various components and additives. Depending on the additives, the oil fluid in the engine unit is divided into: mineral, synthetic and semi-synthetic.
According to its structure, the oil solution is divided into three types:
- . A special feature is its more liquid state, which makes it easier to start the car. During the warm season, the oil solution is not suitable for use, since during operation its viscosity will become less than the standard. The functions of protecting and lubricating units will be reduced to a minimum. Has alphanumeric markings.
- Summer. Used at ambient temperatures above zero degrees. This liquid has a high viscosity and fluidity. Use in winter is not recommended, as the high viscosity will make starting the vehicle difficult. Has digital markings.
- All-season. The most popular type of fluid among all drivers. Can be used at any time of the year at any ambient temperature. Has double marking.
The choice of oil has a direct impact on engine temperature. The power plant ranges from 70 to 90 degrees in winter. As the temperature rises to zero, you can start driving when the engine warms up to 50-70 degrees. In summer, components and assemblies do not need to be warmed up. You can start moving in natural conditions. At the recommended temperature conditions, the engine starts and runs reliably, and the cylinders are filled to the maximum extent. Some types of starters have a normal operating mode at temperatures from 100 to 110 degrees. Basically, this is a wound air-cooled unit, for example a two-stroke engine.
How does the engine lubrication system work?
The task of the lubrication system is to store, transport, clean and supply oil to the rubbing parts of the engine in order to reduce friction of mating parts, ensure a smooth start of the engine and prevent it from overheating. The task is accomplished by a complex of components and assemblies, which includes:
- Engine crankcase (sump) with drain neck.
- Oil pump.
- Oil filter.
- Radiator for cooling oil fluid.
- Pressure reducing valve.
- Pressure meter.
- Temperature sensor.
- Pipelines.
The operating principle of the lubrication system is based on the supply of a combined supply of lubricating fluid to the rubbing parts. Oil supply begins after the engine starts. The pump pumps oil fluid from the engine crankcase and supplies it to the engine for lubrication. After cleaning, the liquid under pressure is supplied to the crank and distribution mechanisms of the engine. Through the connecting rods, the oil solution is supplied to the engine cylinders. The heated oil liquid enters the radiator, where it is cooled. The oil fluid drains from the radiator into the sump.
The remaining components of the power unit are lubricated after creating an oil cloud. It is obtained as a result of the splashing of lubricant by the crank mechanism through the gaps and technological holes. After lubrication, the oil liquid enters the sump, mixing with the oil coming from the radiator, and the lubricant supply process begins anew.
Functionality of lubricating fluids
In order for the power unit to function stably, it is necessary to select the correct lubricant solution. Its selection is made according to parameters, the main of which are:
- Viscosity. The main indicator of any oil. It means the ability of an oil fluid to maintain the proper level of fluidity while covering parts inside the engine. The degree of viscosity depends on the engine temperature and its own. As the temperature rises, the viscosity level drops.
- Viscosity index. A value that determines the level of viscosity of a lubricant solution depending on its temperature. Increasing the viscosity index increases the temperature range in which it can operate. The indicator is different for each type of oil.
- Flash temperature reading. A value that determines the level of low-boiling fractions in the oil liquid. In high-quality oils, flash occurs at temperatures of +230 degrees and above. If the oil solution is of poor quality, then low-viscosity components will quickly burn out and evaporate, and its consumption will increase.
- Boiling temperature reading. An indicator at which an oil fluid loses its viscosity and lubricating properties. Its boiling will lead to contact between the rubbing parts of the power plant and its failure.
- Ignition temperature reading. The amount of critical heating of the oil fluid. Its combustion begins when its temperature reaches +260 degrees. Ignition threatens to cause the engine to explode and cause injury to passengers.
- Volatility. The oil solution begins to evaporate at a temperature of +250 degrees. Determination of volatility is carried out using the NOC method. At the specified temperature, one liter of oil must be boiled for one hour. If after an hour there are 900 grams of liquid left, then the volatility level is 10%. According to international standards, this norm should not exceed 15%.
- Freeze temperature reading. A value that determines the level of loss of fluidity of an oil fluid. When the pour point is reached, the viscosity of the lubricant increases sharply or a process of increasing viscosity occurs with the solidification of paraffin, as a result of which the lubricant hardens.
- Alkaline TVN value. A number that determines the alkaline characteristics of the oil obtained as a result of the addition of detergent and degrading additives. This is an indicator of the ability of an oil fluid to neutralize harmful impurities and acids resulting from the operation of the power plant. A decrease in the alkaline index indicates a decrease in the number of active additives, which can lead to corrosion of the internal parts of the power plant.
- Acid number TAN. An indicator that determines the presence of oxidation elements in the lubricant. An increase in acid number indicates the presence of a large number of oxidation products. The acid number is determined when selecting oil for analysis. Typically, an increased acid value is associated with prolonged operation or high operating temperature of the power plant.
Engine oil operating temperature
The lubricant, depending on its characteristics, can be used in the temperature range from - 50 to + 170 degrees. The operating temperature of the oil in a warm engine and the preservation of its viscosity-technical parameters depend on the temperature regime of the engine. Normal engine temperature ranges from + 80 to + 90 degrees. With such heating, the starting unit has maximum efficiency. Oil lubricant warms up 10-15 degrees more than coolant. Therefore, the operating temperature of engine oil in a warm engine ranges from + 90 to + 105 degrees. It is not recommended to exceed the upper value. This threatens the lubricant with loss of characteristics and rapid wear of rubbing parts.
Changes in engine oil temperature
Engine parts are designed to expand when heated and return to their original state as the engine cools. The operation of the power unit depends on the temperature of the oil in a running engine. Excessively low or high heating of the oil in a running engine has negative consequences.
The low temperature of the lubricant can be considered + 80 degrees. With this indicator, the efficiency of the power plant decreases and its resource decreases. The parts of the power unit will have a slight expansion, which will lead to the formation of gaps between them and a decrease in compression. When the starter is slightly warmed up, moisture can condense and form acids in the lubricant, which will affect the wear of components and assemblies. Low degrees can cause the lubricant to thicken and freeze. This will affect its passage through the filter, creating a vacuum in the lubrication system and difficulties in the operation of the power plant.
High heat is even more dangerous than low heat. Heating the oil fluid above + 105 degrees leads to its viscosity sharply decreasing and fluidity increasing. Under load, the gap between the parts almost disappears, the parts of the crank mechanism come into contact with each other.
When the temperature reaches +125 degrees, the lubricant becomes highly fluid. This allows it to penetrate through the oil scraper rings and burn in the cylinder along with the fuel. The lubricant concentration decreases and its consumption increases. This is unacceptable and leads to wear and tear of the components and assemblies of the power plant.
The starting boiling point of motor oil is + 250 degrees. With this indicator, the lubricant has almost no viscosity, it is in a liquefied state and evaporates well. There is no protective film between the rubbing parts. An indicator that the oil has begun to boil is a sharp increase in temperature, about 3-4 degrees every minute.
Viscosity-temperature characteristics
According to interstate standard 17479.1-85, oils are divided according to viscosity, purpose and performance indicators. Based on viscosity, lubricants are divided into winter and summer classes. The class has a numerical designation; the letter “z” is added to the winter class.
According to their intended purpose, oil fluids are divided into groups that determine the operating mode of power units, with appropriate markings:
- Unforced gasoline and diesel engines. Marked with the letter "A".
- Low-powered gasoline and diesel engines. Marked with the letter “B1” - gasoline, “B2” - diesel.
- Medium-boosted gasoline and diesel engines. Marked with the letter “B1” - gasoline, “B2” - diesel.
- Highly accelerated gasoline and diesel engines operating in various conditions. Marked with the letter “G1, D1” - gasoline, “G2, D2” - diesel, “E1, E2”
The oil marking consists of numbers and letters. For example, the marking M-4з/6В1 means: M – oil, 4 – viscosity class, the letter “z” – winter, 6 – viscosity class in summer, B1 – medium-boosted gasoline power unit. The characteristics are the same as SAE 10w/20 oil.
The viscosity-temperature characteristics of oils according to interstate standard 17479.1-85 and the ratio with SAE are presented in the table:
| Viscosity grade in CIS countries | Highest viscosity at -18C | Viscosity parameters at +100С | SAE classification | |
| minimum | maximum | |||
| 3z | 1200 | 3.8 | 5w | |
| 4z | 2500 | 4.1 | 10w | |
| 5z | 6100 | 5.6 | 15w | |
| 6z | 10500 | 20w | ||
| 6 | 7.0 | 20 | ||
| 8 | 7.0 | 9.5 | 20 | |
| 10 | 9.5 | 11.5 | 30 | |
| 12 | 11.5 | 13.0 | 30 | |
| 14 | 13.0 | 15.0 | 40 | |
| 16 | 15.0 | 18.0 | 40 | |
| 20 | 18.0 | 23.0 | 50 | |
| 3z/8 | 1200 | 7.0 | 9.5 | 5w/20 |
| 4z/6 | 2500 | 5.5 | 7.0 | 10w/20 |
| 4z/8 | 7.0 | 9.5 | ||
| 4z/10 | 9.5 | 11.5 | 10w/30 | |
| 5z/10 | 6100 | |||
| 5z/12 | 11.5 | 13.0 | ||
| 5z/14 | 13.0 | 15.0 | 15w/40 | |
| 6z/10 | 10500 | 9.5 | 11.5 | 20w/30 |
| 6z/14 | 13.0 | 15.0 | ||
| 6z/16 | 15.0 | 18.0 | ||
Conclusion
The presented material showed what types and types of lubricants exist, and what temperature the oil should be in a running engine. It is always necessary to select high-quality lubricant for a car engine. This will prolong its operation and save the owner from early repairs.
When a combustible mixture burns in an internal combustion engine (ICE), heat is generated. Critical temperatures at which damage to thermally loaded parts is possible:
The temperature of the liquid in the cooling system is set within the range - 80 - 90°C. It is supported structurally: a thermostat, a radiator, and a forced cooling fan that turns on based on a signal from the temperature sensor. The engine oil is heated slightly higher - on average to 90 - 100°C.
Oil functions and lubrication modes
Motor oil performs the following tasks:
- removes heat from the friction zone, helping to reduce operating temperature;
- carries away mechanical particles, preventing abrasive wear;
- neutralizes the aggressive environment, preventing corrosive wear;
- inhibits gas breakthrough by sealing the working chamber.
There are 2 main types of oil interaction: boundary and hydrodynamic.
- In the first mode, lubricant flows to the rubbing surfaces without pressure and wets them, reducing wear. The lubricating product is continuously renewed by spraying or using nozzles. In this way the following are lubricated: connecting rod and piston group (including pistons with rings), toothed chain, rockers, valves and a number of other parts.
- Hydrodynamic lubrication - when lubricating fluid is supplied to the friction area from a pressure oil pump. In this case, an oil wedge is formed, causing the internal part to “float” on an oil film, due to which a gap is formed between the surfaces, eliminating direct mechanical contact. An example is the lubrication of crankshaft and camshaft bearings.
The role of lubricating oil viscosity
One of the characteristics of motor oil is its dynamic viscosity, measured in centistokes. This parameter affects the longevity of the car engine and is usually indicated in the vehicle manual.
In addition to the technical features of the engine, seasonal operating temperatures also influence the choice of lubricant viscosity. With increasing temperature, the viscosity of the oil decreases, and with decreasing temperature it increases. Therefore, for winter it should be less, for summer - more.
The most used multi-grade oils contain special components - viscosity additives, designed to provide the required viscosity at elevated temperatures. In addition, it is necessary to maintain the operating temperature of the oil within certain limits.
Negative phenomena in internal combustion engines due to thermal disturbances
The cause of aging of motor oil is the oxidation processes of hydrocarbon group elements occurring in the oil base. In this case, reaction products are released in the form of various deposits: carbon deposits, varnishes, sludge deposits. Temperature conditions have the greatest influence on this.
Soot is a solid substance in the form of soot, which is a product of the oxidation of hydrocarbons. This also includes unburned fuel elements (iron, lead), as well as various mechanical impurities. Carbon deposits cause all sorts of disruptions to the normal working process (detonation, glow ignition and some others).
Varnish is the result of oxidation of the oil film covering the contacting surfaces under the influence of high temperature in the combustion chamber. Up to 80% of its volume is carbon, the rest is oxygen, hydrogen and ash. The varnish coating impairs heat transfer through the oil film and leads to dangerous overheating of the piston and cylinder. The most dangerous is varnish deposits in the piston grooves, leading to ring sticking due to “coking”. The latter is a symbiosis of soot and varnish film.
Sludge is a mixture of products of low-temperature oxidation of carbon compounds with water and emulsion contaminants. The reasons for their occurrence are: insufficient engine temperature, low oil quality, engine design features, as well as operating mode.
Optimal lubricant temperature
Soviet scientists from NAMI have determined the most favorable temperature of a running engine, at which wear of parts is minimal. For both carburetor and diesel engines, it is necessary that the oil temperature in a normally operating engine be in the range of 70 - 80°C.
To achieve the specified values, the coolant on modern engines under normal operating conditions does not heat above 80 - 90°C. Taking this into account, the optimal oil temperature is considered to be 90 - 105 ° C, or 10 - 15 degrees hotter than the cooling medium.
Insufficient operating temperature
If the oil is colder than 90°C, engine efficiency will decrease, with a simultaneous reduction in engine life. Piston skirts cooled by lubricating fluid will expand less than at the design temperature.
Due to the increase in thermal gaps between the piston and cylinder, compression will decrease, which means the efficiency of the working process will decrease. In addition, the lubricant will begin to dilute with fuel, which will lead to the formation of soot and increased fuel consumption.
Another negative consequence of insufficiently heated oil is the release of acids from process waste. There is always moisture in the engine cylinders that comes with atmospheric air. At normal temperatures, water almost completely evaporates.
When the oil is not hot enough, conditions become favorable for acid formation. Acidic components are capable of reacting with light metals, as a result of which the engine will not last the expected period.
The dangers of oil overheating
Excessive heating of the lubricant is much more dangerous than the previous case. Until the operating temperature of the oil leaves the permissible limits, parts operating in the hydrodynamic lubrication mode (crankshaft connecting rods and main journals) do not have mechanical contact with each other.
After heating the oil above 105°C, its viscosity decreases and it becomes more fluid. In this case, under the influence of load, the oil gap loses its load-bearing capacity, and the interacting parts come into contact.
From this moment, due to friction, the rubbing parts begin to heat up, and the thermal gap between them decreases. Increasing oil temperature leads to its oxidation, which theoretically can be detected using laboratory analysis. When the oil heats up above 125°C, it becomes so fluid that it seeps through the oil scraper rings and penetrates into the working cavity of the cylinder, where it burns out.
Due to increasing consumption, oil has to be topped up, in which case all oil additives are renewed, and the analysis results are unreliable. The engine begins to wear out intensively, but this is often attributed to poor performance of the lubrication system.
And only after the engine breaks down can you discover what reason contributed to the sad outcome. If there was an oil starvation, the oil pump would be damaged, and the pistons could be scored. And in this case, the pump is working, but the crankshaft journals are raised.
Concluding the article, I would like to advise drivers who want to maintain the health of their iron “horse” to avoid long-term driving at high speeds, monitor the temperature of the engine oil, change it in a timely manner and fill in a proven product with the viscosity recommended by the automaker.
The principle of operation of an internal combustion engine (ICE) is such that the result of its operation is a large release of heat. The heat inside the engine, especially in its cylinder-piston group, reaches 300°C and higher, if we consider diesel engines. Therefore, the engine oil temperature fluctuates widely as the lubricating fluid moves through the lubrication system inside the internal combustion engine.
Main functions of motor oils
A car engine has many components and parts. Their surfaces are constantly in contact, creating friction between themselves. The result of this phenomenon is increased wear. In addition, friction consumes a significant portion of the engine's efficiency, which is converted into heat.
High temperatures provoke expansion of the materials from which the parts are made. Expansion processes are accompanied by a decrease in the gap between the contacting surfaces. There will come a time when this gap simply disappears, and the internal combustion engine jams - this is what will happen if the unit operates without engine oil.
Engine oil performs a vital function, without which the unit simply cannot operate. It reduces the coefficient of friction by forming a thin oil film between contacting surfaces. In addition, lubricant increases engine efficiency and reduces wear of parts, promotes less heat generation, and also effectively removes it from rubbing surfaces. In addition to these functions, others are implemented:
- By-products of fuel combustion - soot, slag and other deposits - are actively removed thanks to detergent (washing) additives.
- Anti-corrosion protection prevents premature destruction of engine parts from corrosion.
- Dispersing - stabilizing components allow you to remove microscopic insoluble particles by adsorbing them into your composition. They are suspended and removed from the working fluid by a filter.
- The lubricating composition has approximately the same viscosity over a wide temperature range, which is very important for the normal functioning of the engine. This is achieved by using viscosity modifiers or thickening additives. They increase such a parameter as the viscosity index.
- Foaming of a liquid is a very dangerous process that leads to oil starvation of engine parts. To prevent this from happening, anti-foam additives are added to the lubricant composition.
- Depressant additives ensure low viscosity and good fluidity of the oil composition at low temperatures, which allows you to start the engine without problems and lubricate it well until it warms up.
Lubrication system design
The most successful lubrication systems provide different amounts of lubricant, depending on the functional characteristics of the parts. Oil comes to the most critical components and parts under pressure. Less loaded areas receive it by splashing or natural flow. Such lubrication systems are usually called combined.
An oil pump is used to ensure the pressure of the working fluid inside the line. Experiencing such pressure, lubricating fluid from the engine crankcase is supplied to the oil filter. There it is cleaned and supplied to the bearings that ensure the rotation of the crankshaft. Next - to the piston pins, camshaft, valve rocker arms. If there is a turbine, the shaft on which it rotates will need oil. In addition, heat is removed from the inner surface of the pistons. The lubricant seals the gap between the oil scraper rings, as well as the piston compression rings and the engine cylinders, and prevents them from sticking. The liquid gets there, spraying from the nozzles at the bottom of the cylinder-piston block.
Next, the lubricant returns back to the oil pan. Along the way, it is sprayed by the crank mechanism, creating fog. It lubricates all the parts it envelops. From the mist, the lubricant condenses, returning to its original state and position. Thus, the cycle repeats again and again.
Temperature range of oil composition
The operating temperature of the oil varies widely - from ambient air to 180 degrees when passing through the cylinder-piston group. In this case, the metal surfaces of the pistons and cylinders are heated to 300°C. As it circulates through the engine, the oil composition tends to evaporate and burn away. To prevent hydrocarbon vapors from igniting inside the engine, it is necessary that their combustion temperature be higher than the one to which they are usually heated. This ability is determined by such an important parameter as the flash point of the oil.
To determine this parameter, the oil is placed inside the crucible. It is then heated until the fumes begin to flare from the flame. The temperature is immediately measured. Usually it ranges from 220°C and above. This is enough to prevent working fluid vapors from igniting inside the engine. This parameter is not critical, so manufacturers do not indicate on the canisters what the ignition temperature of the oil is.
By the way, diesel vapors ignite at a much lower temperature, about 55–60°C. Having effective water cooling, it is possible to reduce the upper temperature limit of the oil composition to 105–115°C, which is a fairly significant indicator.
Viscosity-temperature characteristics
The stability and efficiency of their operation depends on the viscosity characteristics of lubricants. Viscosity, as well as the viscosity index, are one of the most important indicators, since they change during the transition from very low (-40 ° C) to high operating temperature conditions of the power unit.
According to the classifier of the American Society of Automotive Engineers SAE, motor oils are winter (0W, 5W, 10W, 15W, 20W, 25W), summer (20, 30, 40, 50, 60), as well as all-season, which are commonly used everywhere - for example, 5W30 or 10W40. The diagram shows the temperature ranges for using certain products. A very important indicator is the viscosity level in cold weather, as well as the pour point of the oil. That is, for example, 0W30 lubricant will allow you to start the engine at -40°C, ensuring its normal crankability. 5W30 will do the same down to -35°C and so on.
The diagram shows the temperature ranges for using certain products. A very important indicator is the viscosity level in cold weather, as well as the pour point of the oil. That is, for example, 0W30 lubricant will allow you to start the engine at -40°C, ensuring its normal crankability. 5W30 will do the same down to -35°C and so on.
Overheating of lubricants is very dangerous for the engine. If the composition is heated to +125°C and above, it will lose its viscosity and will not be able to form an oil film. Therefore, it will penetrate into the combustion chamber through the piston rings, burning there along with the fuel. This is how soot deposits form and the lubricant burns out. That is why it is necessary to periodically check the oil level. It happens that a viscosity mismatch leads to lubricant consumption of up to 1 liter per 100–200 kilometers.
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Thermal conditions of a car engine
When a combustible mixture burns in an internal combustion engine (ICE), heat is generated. Critical temperatures at which damage to thermally loaded parts is possible:
The temperature of the liquid in the cooling system is set within the range - 80 - 90°C. It is supported structurally: a thermostat, a radiator, and a forced cooling fan that turns on based on a signal from the temperature sensor. The engine oil is heated slightly higher - on average to 90 - 100°C.
Oil functions and lubrication modes
Motor oil performs the following tasks:
- removes heat from the friction zone, helping to reduce operating temperature;
- carries away mechanical particles, preventing abrasive wear;
- neutralizes the aggressive environment, preventing corrosive wear;
- inhibits gas breakthrough by sealing the working chamber.
There are 2 main types of oil interaction: boundary and hydrodynamic.
- In the first mode, lubricant flows to the rubbing surfaces without pressure and wets them, reducing wear. The lubricating product is continuously renewed by spraying or using nozzles. In this way the following are lubricated: connecting rod and piston group (including pistons with rings), toothed chain, rockers, valves and a number of other parts.
- Hydrodynamic lubrication - when lubricating fluid is supplied to the friction area from a pressure oil pump. In this case, an oil wedge is formed, causing the internal part to “float” on an oil film, due to which a gap is formed between the surfaces, eliminating direct mechanical contact. An example is the lubrication of crankshaft and camshaft bearings.
The role of lubricating oil viscosity
One of the characteristics of motor oil is its dynamic viscosity, measured in centistokes. This parameter affects the longevity of the car engine and is usually indicated in the vehicle manual.
In addition to the technical features of the engine, seasonal operating temperatures also influence the choice of lubricant viscosity. With increasing temperature, the viscosity of the oil decreases, and with decreasing temperature it increases. Therefore, for winter it should be less, for summer - more.
The most used multi-grade oils contain special components - viscosity additives, designed to provide the required viscosity at elevated temperatures. In addition, it is necessary to maintain the operating temperature of the oil within certain limits.
Negative phenomena in internal combustion engines due to thermal disturbances
The cause of aging of motor oil is the oxidation processes of hydrocarbon group elements occurring in the oil base. In this case, reaction products are released in the form of various deposits: carbon deposits, varnishes, sludge deposits. Temperature conditions have the greatest influence on this.
Soot is a solid substance in the form of soot, which is a product of the oxidation of hydrocarbons. This also includes unburned fuel elements (iron, lead), as well as various mechanical impurities. Carbon deposits cause all sorts of disruptions to the normal working process (detonation, glow ignition and some others).
Varnish is the result of oxidation of the oil film covering the contacting surfaces under the influence of high temperature in the combustion chamber. Up to 80% of its volume is carbon, the rest is oxygen, hydrogen and ash. The varnish coating impairs heat transfer through the oil film and leads to dangerous overheating of the piston and cylinder. The most dangerous is varnish deposits in the piston grooves, leading to ring sticking due to “coking”. The latter is a symbiosis of soot and varnish film.
Sludge is a mixture of products of low-temperature oxidation of carbon compounds with water and emulsion contaminants. The reasons for their occurrence are: insufficient engine temperature, low oil quality, engine design features, as well as operating mode.
Optimal lubricant temperature
Soviet scientists from NAMI have determined the most favorable temperature of a running engine, at which wear of parts is minimal. For both carburetor and diesel engines, it is necessary that the oil temperature in a normally operating engine be in the range of 70 - 80°C.
To achieve the specified values, the coolant on modern engines under normal operating conditions does not heat above 80 - 90°C. Taking this into account, the optimal oil temperature is considered to be 90 - 105 ° C, or 10 - 15 degrees hotter than the cooling medium.
Insufficient operating temperature
If the oil is colder than 90°C, engine efficiency will decrease, with a simultaneous reduction in engine life. Piston skirts cooled by lubricating fluid will expand less than at the design temperature.
Due to the increase in thermal gaps between the piston and cylinder, compression will decrease, which means the efficiency of the working process will decrease. In addition, the lubricant will begin to dilute with fuel, which will lead to the formation of soot and increased fuel consumption.
Another negative consequence of insufficiently heated oil is the release of acids from process waste. There is always moisture in the engine cylinders that comes with atmospheric air. At normal temperatures, water almost completely evaporates.
When the oil is not hot enough, conditions become favorable for acid formation. Acidic components are capable of reacting with light metals, as a result of which the engine will not last the expected period.
The dangers of oil overheating
Excessive heating of the lubricant is much more dangerous than the previous case. Until the operating temperature of the oil leaves the permissible limits, parts operating in the hydrodynamic lubrication mode (crankshaft connecting rods and main journals) do not have mechanical contact with each other.
After heating the oil above 105°C, its viscosity decreases and it becomes more fluid. In this case, under the influence of load, the oil gap loses its load-bearing capacity, and the interacting parts come into contact.
From this moment, due to friction, the rubbing parts begin to heat up, and the thermal gap between them decreases. Increasing oil temperature leads to its oxidation, which theoretically can be detected using laboratory analysis. When the oil heats up above 125°C, it becomes so fluid that it seeps through the oil scraper rings and penetrates into the working cavity of the cylinder, where it burns out.
Due to increasing consumption, oil has to be topped up, in which case all oil additives are renewed, and the analysis results are unreliable. The engine begins to wear out intensively, but this is often attributed to poor performance of the lubrication system.
And only after the engine breaks down can you discover what reason contributed to the sad outcome. If there was an oil starvation, the oil pump would be damaged, and the pistons could be scored. And in this case, the pump is working, but the crankshaft journals are raised.
Concluding the article, I would like to advise drivers who want to maintain the health of their iron “horse” to avoid long-term driving at high speeds, monitor the temperature of the engine oil, change it in a timely manner and fill in a proven product with the viscosity recommended by the automaker.
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Engine oil temperature - properties and characteristics
During operation, a car engine withstands significant loads caused by the operation of its components and parts. Therefore, lubricants must be of high quality and meet operating conditions. To protect the power unit from premature failure, you need to know what kind of lubricant needs to be used and what the temperature of the oil in the engine is.
During operation, the temperature of the oil in the engine heats up during operation, withstanding significant loads caused by the operation of its components and parts. Therefore, lubricants must be of high quality and meet operating conditions. To avoid bringing the engine oil to boiling point, you need to know what kind of lubricant to use.
Lubricating fluid is an important component for the operation of any engine. The document defining the classification and designation of oils used in internal combustion engines is the interstate standard GOST 17479-85, as amended in 1999. The requirements of this document are interrelated with the international standards SAE, API and ACEA, which determine the parameters of oils depending on the season and ambient temperature. The SAE standard defines the viscosity-temperature characteristics of a lubricant. The API standard specifies the use of lubricant, depending on the type of engine, its production date and technical parameters (for example, with or without turbocharging). The ACEA standard was developed by European manufacturers. It is similar to the API standard, but has more stringent indicators.
Based on the specified documents, motor oil can be gasoline, diesel and universal. The oil solution is made from mineral oil with the addition of various components and additives. Depending on the additives, the oil fluid in the engine unit is divided into: mineral, synthetic and semi-synthetic.
According to its structure, the oil solution is divided into three types:
- Winter. A special feature is its more liquid state, which makes it easier to start the car. During the warm season, the oil solution is not suitable for use, since during operation its viscosity will become less than the standard. The functions of protecting and lubricating units will be reduced to a minimum. Has alphanumeric markings.
- Summer. Used at ambient temperatures above zero degrees. This liquid has a high viscosity and fluidity. Use in winter is not recommended, as the high viscosity will make starting the vehicle difficult. Has digital markings.
- All-season. The most popular type of fluid among all drivers. Can be used at any time of the year at any ambient temperature. Has double marking.
The choice of oil has a direct impact on engine temperature. The operating temperature of the power plant ranges from 70 to 90 degrees in winter. As the temperature rises to zero, you can start driving when the engine warms up to 50-70 degrees. In summer, components and assemblies do not need to be warmed up. You can start moving in natural conditions. At the recommended temperature conditions, the engine starts and runs reliably, and the cylinders are filled to the maximum extent. Some types of starters have a normal operating mode at temperatures from 100 to 110 degrees. Basically, this is a wound air-cooled unit, for example a two-stroke engine.
How does the engine lubrication system work?
The task of the lubrication system is to store, transport, clean and supply oil to the rubbing parts of the engine in order to reduce friction of mating parts, ensure a smooth start of the engine and prevent it from overheating. The task is accomplished by a complex of components and assemblies, which includes:
- Engine crankcase (sump) with drain neck.
- Oil pump.
- Oil filter.
- Radiator for cooling oil fluid.
- Pressure reducing valve.
- Pressure meter.
- Temperature sensor.
- Pipelines.
The operating principle of the lubrication system is based on the supply of a combined supply of lubricating fluid to the rubbing parts. Oil supply begins after the engine starts. The pump pumps oil fluid from the engine crankcase and supplies it to the lubrication filter. After cleaning, the liquid under pressure is supplied to the crank and distribution mechanisms of the engine. Through the connecting rods, the oil solution is supplied to the engine cylinders. The heated oil liquid enters the radiator, where it is cooled. The oil fluid drains from the radiator into the sump.
The remaining components of the power unit are lubricated after creating an oil cloud. It is obtained as a result of the splashing of lubricant by the crank mechanism through the gaps and technological holes. After lubrication, the oil liquid enters the sump, mixing with the oil coming from the radiator, and the lubricant supply process begins anew.
Functionality of lubricating fluids
In order for the power unit to function stably, it is necessary to select the correct lubricant solution. Its selection is made according to parameters, the main of which are:
- Viscosity. The main indicator of any oil. It means the ability of an oil fluid to maintain the proper level of fluidity while covering parts inside the engine. The degree of viscosity depends on the engine temperature and its own. As the temperature rises, the viscosity level drops.
- Viscosity index. A value that determines the level of viscosity of a lubricant solution depending on its temperature. Increasing the viscosity index increases the temperature range in which it can operate. The indicator is different for each type of oil.
- Flash temperature reading. A value that determines the level of low-boiling fractions in the oil liquid. In high-quality oils, flash occurs at temperatures of +230 degrees and above. If the oil solution is of poor quality, then low-viscosity components will quickly burn out and evaporate, and its consumption will increase.
- Boiling temperature reading. An indicator at which an oil fluid loses its viscosity and lubricating properties. Its boiling will lead to contact between the rubbing parts of the power plant and its failure.
- Ignition temperature reading. The amount of critical heating of the oil fluid. Its combustion begins when its temperature reaches +260 degrees. Ignition threatens to cause the engine to explode and cause injury to passengers.
- Volatility. The oil solution begins to evaporate at a temperature of +250 degrees. Determination of volatility is carried out using the NOC method. At the specified temperature, one liter of oil must be boiled for one hour. If after an hour there are 900 grams of liquid left, then the volatility level is 10%. According to international standards, this norm should not exceed 15%.
- Freeze temperature reading. A value that determines the level of loss of fluidity of an oil fluid. When the pour point is reached, the viscosity of the lubricant increases sharply or a process of increasing viscosity occurs with the solidification of paraffin, as a result of which the lubricant hardens.
- Alkaline TVN value. A number that determines the alkaline characteristics of the oil obtained as a result of the addition of detergent and degrading additives. This is an indicator of the ability of an oil fluid to neutralize harmful impurities and acids resulting from the operation of the power plant. A decrease in the alkaline index indicates a decrease in the number of active additives, which can lead to corrosion of the internal parts of the power plant.
- Acid number TAN. An indicator that determines the presence of oxidation elements in the lubricant. An increase in acid number indicates the presence of a large number of oxidation products. The acid number is determined when selecting oil for analysis. Typically, an increased acid value is associated with prolonged operation or high operating temperature of the power plant.
A number of requirements are imposed on lubricants used in a car and on motor oil in particular, which are associated not only with the characteristics of the physical and chemical processes occurring during engine operation, but also with operating conditions.
In order to have an idea of what factors affect internal combustion engine lubricants, you should consider the basic concepts that describe temperature-dependent properties:
- Flash point (t°);
- boiling temperature;
- Operating t°.
Temperature
Lubricants are used to prevent dry contact between the moving parts of internal combustion engines. They are designed to create a sliding boundary and separate rubbing parts. Flash point is related to a parameter such as evaporation.
Motor lubricant has a number of characteristics, including viscosity. Viscosity directly depends on temperature. The operating temperature range of the internal combustion engine forces manufacturers to take into account the change in viscosity from the moment the engine is started until it reaches the optimal mode.
Engine lubrication system
The rubbing parts of the internal combustion engine are lubricated continuously during its operation. The simplest system consists of an oil pump that provides circulation, a filter and channels in the cylinder head and block, crankshaft, etc., through which lubricant is supplied to the contact points. As a rule, the lubrication system has several sensors that monitor the most important parameters of the system:
- Level sensor - notifies the driver that the level has dropped and requires replenishment or replacement;
- Temperature sensor - mainly found on sports cars, the engines of which are constantly under enormous load;
- Pressure sensor - warns of a drop in pressure in the lubrication system. The cause may be a clogged or faulty filter or a clogged oil line.
Determination of volatility
To determine the temperature at which light hydrocarbon vapors contained in motor oil flash, it is heated in a special crucible until the vapors begin to flash from an open flame. There is no flash in a running engine, but the lubricant can evaporate and so-called waste occurs. This is a slow and imperceptible process, and the oil level sensor ultimately only states a fact. The method for determining flash t° is regulated by GOST 6356.
Motor lubricant has two interdependent characteristics - viscosity and temperature. With increasing temperature, the viscosity decreases and vice versa, at low temperatures it becomes more viscous. In the description of the lubricant, both parameters are always indicated in the performance characteristics.
Flashes of volatile hydrocarbons occur when a certain temperature is reached, beyond which the process of boiling and evaporation begins. A flash t° of 225° Celsius and above is considered a good indicator; for comparison, diesel fuel vapors flare up at +55°. Low-quality petroleum products with low viscosity contain a large percentage of light fractions that burn out and, as a result, the volume of lubricating fluid decreases, as reported by the sensor.
Flash point is a characteristic that is largely used in laboratory and industrial use, and which the vast majority of car owners do not pay attention to. Manufacturers also do not focus consumers’ attention on the flash point, not indicating it on the packaging of motor oils.
terms of Use
The operating temperature range of motor oil is from -40 to +180 degrees. The industry produces motor lubricants with different viscosity-temperature characteristics that correspond to the required parameters, which in turn are dictated by the characteristics of the power plant and climate. Thus, in a diesel internal combustion engine there are different conditions, higher temperatures and fuel composition, requiring motor oils of a special formulation. The characteristics of a motor lubricator may vary depending on the structure of its base and a set of modifying additive components that prevent the oil from becoming more or less viscous under different temperature conditions, while maintaining lubricating properties. Parameters such as crankability and pumpability depend on environmental conditions.
Low temperature oils
The properties of low-temperature motor lubricants allow the vehicle to be operated in cold climatic conditions, while maintaining all optimal operating parameters - viscosity, fluidity and adhesion to metal surfaces. 
It is known that the engine lubrication system operates in two modes simultaneously, lubricating rubbing parts under pressure and without pressure. The pressure is provided by a gear rotary or other type pump.
Under pressure, the surfaces of the crankshaft and camshaft and other engine components are usually lubricated; drip lubrication of the pistons occurs due to the splashing of oil by moving parts. At low temperatures, it becomes thicker and the force on the starter to turn the crankshaft increases, the engine has difficulty starting and the “oil pressure” sensor lights up. The lubricant hardens due to the hydrocarbons it contains of paraffin origin with a high boiling point, which tend to crystallize at low temperatures. Low-temperature lubricants contain a small amount of paraffin hydrocarbons and special additives that do not allow the lubricant to thicken in cold weather. To heat up the engine oil, some brands of cars have a forced crankcase heating function, which makes cold starting easier.
Effect of high temperatures
The transition of a substance from a liquid to a gaseous state can be expressed by simple evaporation or occur in the boiling phase of the liquid. The boiling range of most motor lubricants lies outside the normal operating parameters of the internal combustion engine.
High temperatures in the combustion chamber decompose lubricant particles trapped there into simple compounds in the form of soot, part of which is carried away by exhaust gases, and part of which settles as carbon deposits on the rings and piston. High-temperature oxidation processes of motor oils contribute to the formation of varnish deposits on the internal surfaces of the engine. The lower the quality of the motor oil, the lower its boiling point.
In automobile internal combustion engines, cooling is usually liquid. The temperature sensor on most cars is triggered when a threshold value of 85-90 degrees is reached, including forced engine cooling. The engine cooling system is structurally adjacent to the lubrication system, so in order for the engine oil to boil, you will need to warm up the engine to a temperature at which the coolant begins to evaporate first. For reference, the average boiling point of ethylene glycol-based antifreeze is 120-125 Celsius.
Reducing engine oil temperature
In sports cars with high-performance gasoline engines, the temperature of the engine oil should not exceed the operating temperature limits. To avoid overheating of the oil, a cooling system is installed on the power unit, consisting of an oil cooler, pipelines and a special adapter for the oil filter. A temperature sensor is often installed in the same circuit if the machine is not equipped with one from the factory. This additional cooling function contributes to better heat dissipation of the motor operating under heavy load.
Understanding terms such as flash point, viscosity, thermal conditions and operating temperature range is just the minimum knowledge about motor lubrication that a car enthusiast needs. If we consider each parameter in more depth, we can find out that the flash point of, say, synthetic oils is on average lower than that of natural ones. Behind the physical processes are chemical transformations of complex substances, which a temperature sensor or oil pressure sensor will not tell you about; developers spend huge amounts of money on creating new chemical additive compounds that improve the properties of lubricants.
Conclusion
The vehicle's operating manual usually indicates the types of fluids used, including internal combustion engine lubricants. Deviation from the recommended parameters can lead to overheating and premature wear of the mechanisms.
